This invention relates in general to the precision mating of two elements, more particularly, to the making of cast models, such as for the precise fabrication of models of teeth, gums and jaws.
The prior art method for fabricating dental models necessitates the conventional manipulation of a patient's negative impression to ultimately obtain a positive model with removable tooth segments and dies. In prior art practice, many time-consuming steps and much skill is required to manually set various types of pins into the tooth, gum or jaw facsimile. This requires interposing bushings, sleeves or guides into matching holes which are usually incorporated into a base. It is customary to construct the latter at the time the model is poured, using gypsum, epoxy, putty or other moulding materials.
Prior art methods for constructing crowns, inlays, bridges, dentures, etc., either in composite or individually, necessitate the ability to remove each individual segment (tooth-die) from its spatial physical relationship to the remainder of the jaw model for the purpose of constructing accurate margins and contours. In the event that two or more individual units of bridgework are to be joined, either by a one piece casting, solder joint, sticky-wax, coping, or a precision attachment, it is necessary that the working model segments be accurately and repeatedly returned to their original relationships precisely as it or they existed prior to any cutting, separations or disassembly of the jaw model.
In prior art practice, such working models are constructed by the following tedious, inefficient and precious-time consuming steps:
(1) Painstakingly placing a pin, pins, or bushings into or over the negative cavity of the tooth in the impression by "eyeballing" and guaging it with respect to the vertical axis of each adjacent negative tooth cavity while avoiding physical contact with the patient's negative mouth impression or adjacent pins;
(2) Using some method (normally a cross-wire, hot wax, a holding mechanism or other gadget) to "freeze" the pin or sleeve in the position it was placed; and
(3) Pouring liquid gypsum or other setting material into the mold and waiting for it to polymerize, crystalize, set or harden. The so-called "first pour" then hardens thereby imprisoning the pins, sleeves or bushings rigidly, as they were placed or positioned manually, mechanically, visually or otherwise.
(4) After these pins or devices are set rigidly in position by the hardening of the first pour, a releasing, anti-seizing or separating medium must first be carefully coated over the gypsum or whatever was used as a moulding compound. This permits essential future separation, and a second pour is then made.
(5) After the second pour hardens, the working model is removed from the original negative impression, prepared for placement or acceptance on an articulator platform and sectioned. Sectioning facilitates the removal and consequent replacement of the individual dies. On occasion, during their removal, or during efforts to effect separation, the two halves fracture or break apart and the formerly rigid pins either bend, loosen, collapse, or dislodge due to loss of perimeter support.
Common methods presently used in the construction of such models require the skillful and experienced application of judgment in the positioning of pins or guides, either manually or mechanically, the use of unhardened liquid moulding materials, such as for example, gypsum, and the "trial and error" positioning of pins, bushings or dressed models to capture the desired location and parallelism. Therefore, a working time limit and "critical" situation is established. If any step is affected by either judgmental or mechanical error, defective materials such as faulty, nonhomogeneous, or contaminated mixtures, etc., or environmental influences, such as temperature, moisture, or the inadvertent movement, dislodgement or displacement of the pins or guides during pouring, the entire procedure fails. This necessitates the dentist taking a second impression of the patient's teeth, gum, jaw or mouth (a situation professionally embarrassing and uncomplimentary, since it extends extra imposition and inconvenience to the patient, requiring a revisit to the dentist's office).
Whatever methods are in use or utilized in the prior art, the following problems consistantly exist:
(1) "Eyeballing", the use of gadgets, mechanical devices or other apparatus are required on the part of the operator to properly align the reference pins. The methods used are tedious, time consuming, expensive and inefficient.
(2) Unhardened gypsum or other moudling compounds are normally required for the process of securing incorporated male and female "pins" or bushings in preparing models. These systems at best are difficult to control, and are oftentimes nonreversible.
(3) Critical and time-expensive setbacks occur in the nature of such methods, such as difficulty in establishing parallelism of two or more segments, in keeping deep female sections free of often unavoidable foreign debris, not to mention shrinkage, warpage, fusing, the wear of gypsum or other materials which harden during the procedure.
(4) Inadvertent separation of the two adjacent sections may occur in a model thinly held together by virtually only the metal or plastic locating or positioning pins, thereby causing the entire first and second pours to be separated from the impression material.
It is therefore a broad object of this present invention to improve the entire fabrication of cast models, and more particularly of model teeth, gums and jaws.
A more particular object of this invention is to facilitate the removal and precise return of individual segments of a hardened dental casting to its or their original positional relationship, during processing.
Other objects of this invention are to eliminate the tedious and painstaking manipulation of pins, bushings, guides, mechanical aids, or the use of other expedients, such as hot wax, sprues, mechanical holding devices, other gadgets, or the successive pourings of setting materials into the mold for the purpose of securing reference-type aids or elements for the casting.
These and many other objects are realized in the present invention which comprises a prefabricated sandwich which is constructed to accept a cast model such as of teeth, gums and jaws. In preferred form, this sandwich consists of a pair of precision plates including a mounting plate and lower mating plate and into the mating surfaces of which are incorporated a profuse and extended interdigitation of geometric patterns of varying depths and sizes. The hardened model of the jaw is merely glued, fastened or otherwise secured to the mounting plate for processing. The remaining half, or lower mating plate, forms its base.
In accordance with this present invention, the precision plates of the pair are preferably formed so as to be completely interchangeable (any upper mounting plate fitting any lower mating plate). They invariably mate together snugly to provide a fixed registration. Unrestricted compound cuts and required separations may be executed on the cast model clean through the plate section upon which the model is fastened without destroying the segment's replacement accuracy. Since each half or individual plate of the mating sandwich is precisely fabricated by the manufacturers in advance, and constructed of durable materials, they are not subject to technician or operator error. Normal environmental factors such as temperature, humidity, nonhomogeneous gypsum or other moulding mixes, or foreign contaminents in dirty water may no longer be of concern. No pins, bushings, sleeves, drilling or boring by mechanical means and other similar procedures are any longer required in the construction of dies of the types described. The original precision mating fit of the mating plates remains constant throughout the entire working procedure.
After the hardened model of the teeth is secured to the proper surface of the precision mating plates of the present invention, the individual teeth and edentulous areas, if applicable, are sectioned only as far as needed to permit cutting through the mounting plate. The lower mating plate need not be cut or sawed into. In fact, the model, complete with the fastened upper mounting plate, may be lifted clear of the lower mating plate and placed to the side; and separation by cutting or sawing may be carried out in this manner. With the use of this highly versatile device, each and every section is immediately contiguous with each other section; therefore, any quadrant or an entire half a section of the "arch-model", once it's fastened to the mounting half section of the precision mating plates, may be cut through and removed from the line of saw or cutting blade travel if it appears that it will be in the way or an obstacle during the course of starting cuts or separations on the opposite side or section.
All, and any individual segments, quadrants, or half sections can also be removed individually, or simultaneously, as needed, from an entire upper or entire lower dental plate, for trial of a one-piece bridge consisting of two or more units, or for soldering. With prior art methods, this is not as readily or as easily possible. The structure of the present invention also facilitates mounting and repositioning the various elements or composites to articulators. The lower mating plate has a configured geometric pattern and a keyed protuberance incorporated on the underside for engagement by whatever method of fastening, bonding, holding, latching, or clamping that one may elect to utilize. For example, gypsum, plasters, glues, adhesives, or mechanically designed key-ways, clamps, latches or magnetic assisting or adhering devices may be chosen.
In accordance with another feature of the present invention, the precision mating plates may be provided with built-in venting openings to the underside of each of the elements of a pattern to eliminate the inadvertent or sporadic possible trapping of debris inside the geometric patterns which might otherwise prevent their precise seating or joining. As a further feature to facilitate accuracy, the mating plates may be keyed, indexed and/or color coded on their inner and/or outer perimeter edges, so that an immediate visual identification permits placement of appropriate segments or sections to the correct quadrant or location without "trial and error" locating techniques. Also, notchings may be provided around the outer edges in between the two mating plates which may serve to assist in the quick removal and separation of individual sections when needed. A further desirable feature which may be incorporated as part of the combination of the present invention is a slightly extended overhang of adequate cross section located along the outer and inner perimeter of the upper mounting plate that holds the model. This feature not only provides a grasping ledge which permits the operator to avoid excessive fingering of the work die on its critical surface areas, but it also helps avoid rocking or prying adjacent segments off their respective seats.
Applicant's device has a multitude of advantages over prior art methods, gadgets and apparatus available for prefabricating the processing cast models, particularly models of teeth, gums, and jaws. Once any model, be it teeth, gum or jaw section, has been attached or fastened to the mounting plate, individual sections can be promptly cut, removed and worked upon an indefinite number of times and precisely replaced in exact spatial relationship to the other elements of the model as it originally existed, without need for the exercise of constant caution, care and anxiety on the part of the operator, and without the detrimental wear and tear and consequent loss of accuracy due to looseness developing in one or more individual die segments.
Other objects, features and advantages will readily appear to those skilled in the art after a study of the detailed description hereinafter with reference to the attached drawings.